Don't know why I never thought of doing it before, but yesterday I hooked up a Shure SM58 and my Taylor acoustic/electric to my Mackie ProFX12 mixer, then sent the output to the CD/MP3 input on the back of the Spider.

Voila! - Instant PA System!

I did find out, though, that if I only fed 1 side of the left/right mixer output to the stereo input that the volume was not very loud, but when I sent a full stereo signal (I used the headphone output because I only had an adapter to do it that way), the volume was huge - and clear!

Most likely I would never use the amp this way, but it's a good option as I don't have any powered PA speakers of my own to use, and it would make an ideal monitor, too.

Good idea, Mike! I just ordered the same mixer from Sweetwater yesterday so I can do the same thing! Been using a Fender portable amp (the little package they market for that sort of thing), but now I can carry the mixer instead, and plug my wireless headset into that, and my guitar into the Spider IV 75, and not have to mess with that other amp.

(Later...) decided not to use the headphone-to-mp3 in - I'm just running the guitar into Input 1 (with the High Z button depressed), the headset into Input 2, and the left out into the (guitar) input of the Spider IV. Works like a charm.

As an aside, my Spider IV sits under my computer desk, as that's where I normally play. My computer headphone jack is connected to the mp3 in on the Spider (so I can play along with iTunes or videos on the 'puter), and my JTV-59 into the guitar input on the Spider. I'm really lovin' it!